

package usocalculadora;
import java.util.Vector;

/**
 * Es la clase que implementa el Stack<E>
 * @author Andrea Magaly
 */
public class Pila<E> implements Stack<E>{

 protected Vector<E> data;
 
 public Pila()
 // post: constructs a new, empty stack
 {
   data=new Vector<E>();  
   
 }
 
 public void push(E item)
	// post: the value is added to the stack
	// will be popped next if no intervening push
	{
		data.add(item);
               
	}
 
 public E pop()
	// pre: stack is not empty
	// post: most recently pushed item is removed and returned
	{
		return data.remove(size()-1);
	}
 
 public E peek()
	// pre: stack is not empty
	// post: top value (next to be popped) is returned
	{
		return data.get(size() - 1);
	}
	
	public int size()
	// post: returns the number of elements in the stack
	{
		return data.size();
	}
  
	public boolean empty()
	// post: returns true if and only if the stack is empty
	{
		return size() == 0;
	}
    
}
